Typically, during refueling of a nuclear reactor, the space above the reactor vessel is flooded with boric acid to protect those working in the vicinity from radiation. The boric acid is extremely corrosive. Hence, it is desirable to plug the stud holes in the flange attached to the reactor vessel after the bolts holding the reactor vessel head (cover) have been removed but prior to flooding. Moreover, it is desirable to plug the stud holes before the cover is removed. Hence, stud hole plugs must be designed to pass through the holes in the flange of the reactor head.
Prior threaded plugs have been found to be difficult and time consuming to install and ineffective. For this reason, those in the art have sought to develope plugs without threads. See, for example, U.S. Pat. Nos. 4,312,708 and 4,671,518.